It’s [Still!] the SQL Injection… Stupid

Did you see Imperva’s October 2012 Hacker Intelligence Report? The report is a data mining study directed toward the on-line forum behaviors among a purportedly representative group of hackers. The milestone for October 2012 is that Imperva now has a year’s worth of data upon which to report. Almost a half a million threads in the mine. In this study, keyword analysis found SQL injection sharing the top of the heap with DDOS in terms of what hackers talk about in the forums. In the wake of Powershell 3.0 – the study also identifies shell code as the big up-and-comer for mentions in the hacker threads. Only 11% of the forum posts mention “brute force”. “Brute force” being the only topical category Imperva charted with a direct relationship to cryptography.

The absence of an aggregate specifically dedicated to cryptography or encryption strongly suggest the hackers are not talking much about cryptography. Hmmmm.

Keyword frequency in 439,587 forum threads:

  1. SQL injection 19%
  2. dDos 19%
  3. shell code 15%
  4. spam 14%
  5. XXS 12%
  6. brute force 11%
  7. HTML injection 9%

The report also cites disturbing data from a 2012 Gartner study, “Worldwide Spending on Security by Technology Segment, Country and Region, 2010-2016″. The Gartner study purportedly finds that less than 5% of money spent on computing security products buys products that are useful against SQL injection.

Holy octopus slippers! The statistics definitely make a good case for taking a look at Imperva’s products. Even if there is some marketing bias in the study – I don’t think so, but saying even if there is – the findings are more bad news for data security. Whats worse is we seem to be headed in the wrong direction.  Consider:

  • The SQL Server 2008 Books Online had a page of SQL injection prevention best practices that is removed from the SQL Server 2012 edition.
  • SQL injection prevention guidance is largely unchanged for many years yet is not widely followed. Input validation is the key. Judging by the hacker interest in SQL injection, adoption of the guidance must be low.
  • Hackmageddon.com’s Cyber Attack Statistics indicate that SQL injection is found in over 25% of the hacker attacks documented during October 2012.
  • Cloud host FireHost – a WMWare base web host with an impressive security claim and a data centers in Phoenix, Dallas, London and Amsterdam –  reported that attacks the Firehost infrastructure had detected and defend saw a 69% spike in SQL injection attacks in second quarter 2012 ( and then cross site scripting surged in just ended Q3).

What is stopping us from truly going after this problem? Input validation is not hard and need not be a bottleneck. Threat detection is supposedly a part of any ACE/PCI/FIPS/HIPPA  compliant system. Detection avoidance is well understood. Nonetheless, and for reason$ far beyond reasonable, the strategic emphasis remains stuck on compliance. That would be OK if the standards of compliance were even close to adequate. Clearly they are not. That proof is in the pudding.

There are SQL injection detection and avoidance products out there that work. Many many products. Just to name a few – and by way of describing the types of tools that forward thinking organizations are already buying in an effort to eradicate SQL injection:

Application Delivery Network (ADN)

  • Citrix NetScaler
  • F5s BigIP
  • Fortinet  FortiGate

Web Application Firewall (WAF)

  • Applicature dotDefender WAF
  • Cisco ACE Web Application Firwewall
  • Imperva Web Application Firewall & Cloud WAF
  • Barracuda Networks Web Application Firewall
  • armorize’s SmartWAF (Web server host based)

Web Vulnerability Scanners (WVS)

  • sqlmap (free)
  • Acunetix WVS

Unified Threat Management (UTM)

  • Checkpoint UTM-1 Total Security Appliance
  • Saphos UTM Web Server Protection
  • Watchguard XTM

These products and the overarching practice changes needed to implement them show success in going after the problem. But, as the Gartner study shows, nobody seems to be buying it.

There are also cloudy platform hosts and ISPs like FireHost that handle the WAF for organizations that cannot justify the capital costs and FTEs required to do the job right in-house due to scale.

Ever so slowly the major hosts are imposing WAF upon all tenants. Another n years at the current snail’s pace and the security improvement just might be noticeable. Seems to me like “do it and and do it now” is the only choice that can reverse a ridiculous situation that has gone on too long already. Even secure hosts prioritize profitability over basic security. That is rent seeking.

Any web presence that takes another tact is telegraphing priorities that violate the duty to protect that which is borrowed under an explicit promise of confidentiality or generally accepted fiduciary performance levels equivalent to all other financial and intellectual assets of that organization. Few meet the sniff test. Many remain highly profitable. Just take a look in your Facebook mirror. Customer’s and consumers have no visibility into how any organization will honor this responsibility nor recourse when that duty is shirked. The metrics above make clear that poor security practices shirk the responsibility and carelessly feed the identity theft racket. It must end. Organizations that perpetuate this status quo and remain profitable are complicit in an ongoing crime of  against humanity. IT staff who are fairly characterized as “team players” or leaders in such organizations are every bit as culpable as the soldiers of Auschwitcz or My Lai or the owner of a piano with Ivory keys.

Organizations private and public have a fundamental obligation to protect customers, clients and citizens from illegal exploitation. What in the world makes it OK to exclude chronic identity theft violations from that responsibility?

Even when the data center budget includes one of the more robust solutions; to have done the needful in terms of basic input validation, code/user authentication and principal-of-least-privilege access rights is essential for any good defense-in-depth security strategy.

Consider this T-SQL function from the Encryption Hierarchy Administration schema that implements a passphrase hardness test based upon the SQL injection prevention guidance in the SQL 2008 BOL.

1   -------------------------------------------------------------------------------
2   --    bwunder at yahoo dot com
3   --    Desc: password/passphrase gauntlet
4   --    phrases are frequently used in dynamic SQL so SQL Injection is risk
5   -------------------------------------------------------------------------------
6   CREATE FUNCTION $(EHA_SCHEMA).CheckPhrase 
7     ( @tvp AS NAMEVALUETYPE READONLY )
8   RETURNS @metatvp TABLE 
9     ( Status NVARCHAR (36)
10    , Signature VARBINARY (128) )
11  $(WITH_OPTIONS)
12  AS
13  BEGIN
14    DECLARE @Status NVARCHAR (36)
15          , @Name NVARCHAR(448)
16          , @UpValue NVARCHAR (128) 
17          , @Value NVARCHAR (128) ;
18    -- dft password policy as described in 2008R2 BOL + SQL Injection black list
19    -- fyi: SELECT CAST(NEWID() AS VARCHAR(128)) returns a valid password 
20    SET @Status = 'authenticity';
21    IF EXISTS ( SELECT *
22                FROM sys.certificates c
23                JOIN sys.crypt_properties cp
24                ON c.thumbprint = cp.thumbprint
25                CROSS JOIN sys.database_role_members r
26                WHERE r.role_principal_id = DATABASE_PRINCIPAL_ID ( '$(SPOKE_ADMIN_ROLE)' ) 
27                AND r.member_principal_id = DATABASE_PRINCIPAL_ID ( ORIGINAL_LOGIN() )  
28                AND c.name = '$(OBJECT_CERTIFICATE)'
29              AND c.pvt_key_encryption_type = 'PW'
30                AND cp.major_id = @@PROCID 
31                AND @@NESTLEVEL > 1 -- no direct exec of function 
32                AND IS_OBJECTSIGNED('OBJECT', @@PROCID, 'CERTIFICATE', c.thumbprint) = 1
33                AND EXISTS ( SELECT * FROM sys.database_role_members 
34                              WHERE [role_principal_id] = USER_ID('$(SPOKE_ADMIN_ROLE)')
35                              AND USER_NAME ([member_principal_id]) = SYSTEM_USER 
36                              AND SYSTEM_USER = ORIGINAL_LOGIN() ) )        
37      BEGIN
38        SET @Status = 'decode';
39        SET @Name = ( SELECT DECRYPTBYKEY( Name 
40                                         , 1
41                                         , CAST( KEY_GUID('$(SESSION_SYMMETRIC_KEY)') AS NVARCHAR (36) ) ) 
42        FROM @tvp );
43        SET @Value = ( SELECT DECRYPTBYKEY( Value, 1, @Name ) FROM @tvp );                    
44        IF PATINDEX('%.CONFIG', UPPER(@Name) )  -- no strength test, will fall through 
45         + PATINDEX('%.IDENTITY', UPPER(@Name) )             
46         + PATINDEX('%.PRIVATE', UPPER(@Name) ) 
47         + PATINDEX('%.SALT', UPPER(@Name) )           
48         + PATINDEX('%.SOURCE', UPPER(@Name) ) > 0       
49          SET @Status = 'OK';
50        ELSE
51          BEGIN
52            SET @UpValue = UPPER(@Value);
53            SET @Status = 'strength';
54            IF ( (    ( LEN(@Value) >= $(MIN_PHRASE_LENGTH) )   -- more is better
55                  AND ( PATINDEX('%[#,.;:]%'
56                      , @Value ) = 0 )   -- none of these symbols as recommended in BOL 
57                  AND ( SELECT CASE WHEN PATINDEX('%[A-Z]%'
58                                                  , @Value) > 0 
59                                    THEN 1 ELSE 0 END    -- has uppercase
60                              + CASE WHEN PATINDEX('%[a-z]%'
61                                                  , @Value) > 0 
62                                    THEN 1 ELSE 0 END    -- has lowercase  
63                              + CASE WHEN PATINDEX('%[0-9]%'
64                                                  , @Value) > 0 
65                                  THEN 1 ELSE 0 END    -- has number
66                              + CASE WHEN PATINDEX('%^[A-Z], ^[a-z], ^[0-9]%' -- has special
67                                                  , REPLACE( @Value,SPACE(1),'' ) ) 
68                       ) > 0  
69                                    THEN 1 ELSE 0 END ) > 2 ) )   -- at least 3 of 4
70              BEGIN 
71                -- black list is not so strong but can look for the obvious 
72                SET @Status = 'injection';                       
73                IF ( PATINDEX('%[__"'']%', @UpValue)   -- underscore (so no sp_ or xp_) or quotes
74                   + PATINDEX('%DROP%'   , @UpValue)   -- multi-character commands... 
75                   + PATINDEX('%ADD%'    , @UpValue)
76                   + PATINDEX('%CREATE%' , @UpValue)
77                   + PATINDEX('%SELECT%' , @UpValue)
78                   + PATINDEX('%INSERT%' , @UpValue)
79                   + PATINDEX('%UPDATE%' , @UpValue)
80                   + PATINDEX('%DELETE%' , @UpValue)
81                   + PATINDEX('%GRANT%'  , @UpValue)
82                   + PATINDEX('%REVOKE%' , @UpValue)
83                   + PATINDEX('%RUNAS%'  , @UpValue)
84                   + PATINDEX('%ALTER%'  , @UpValue)
85                   + PATINDEX('%EXEC%'   , @UpValue)
86                   + PATINDEX('%--%'     , @Value)     -- comments...
87                   + PATINDEX('%**/%'    , @Value) 
88                   + PATINDEX('%/**%'    , @Value)  = 0 )
89                  BEGIN 
90                    SET @Status = 'duplicate';
91                    IF NOT EXISTS ( SELECT *                  -- not already used  
92                                    FROM $(EHA_SCHEMA).$(NAMEVALUES_TABLE) n
93                                    WHERE ValueBucket = $(EHA_SCHEMA).AddSalt( '$(SPOKE_DATABASE)'
94                                                                              , '$(EHA_SCHEMA)'
95                                                                              , '$(NAMEVALUES_TABLE)'
96                                                                              , 'ValueBucket' 
97                                                                              , @Value)
98                                    AND CAST(DecryptByKey( n.Value -- should be rare
99                                                          , 1
100                                                         , @Name ) AS NVARCHAR (128) )  =  @Value )  
101                     SET @Status = 'OK';
102                 END
103             END
104          END
105     END
106   INSERT @metatvp
107     ( Status
108     , Signature ) 
109   VALUES 
110     ( @Status
111    , SignByCert( CERT_ID('$(AUTHENTICITY_CERTIFICATE)'), @Status ) );
112   RETURN;
113 END
114 GO
115 ADD SIGNATURE TO $(EHA_SCHEMA).CheckPhrase 
116 BY CERTIFICATE $(OBJECT_CERTIFICATE)
117 WITH PASSWORD = '$(OBJECT_CERTIFICATE_ENCRYPTION_PHRASE)';
118 GO

SQL injection input validation is only part of what goes on here. The function accepts an already encrypted name value pair TVP as a parameter and returns a signed business rule validation result as a TVP.  To do so, first the schema and user authenticity are verified before the phrase is decoded and the SQL injection/detection rules are applied. Only if all rules are met will an IO be required to verify that the phrase has not already been used.

The bi-directional encoding of parameters with a private session scoped symmetric key helps to narrow the SQL injection threat vector even before the filter(s) can be applied. This means that the passed values have already successfully been used in a T-SQL ENCRYPTBYKEY command in the current database session. Not that encryption does anything to prevent or detect SQL injection. It is more that the first touch of any user input value carries higher risk. Likewise the first use of an input in any dynamic SQL  statement carries a higher risk. Always better to do something benign with user input before you risk rubbing it against your data.

In the process of validation, two black lists are used to filter punctuation (line 55) and specific character sequences (lines 73-88) frequently identified as injection markers.

Another function from the schema validates names for T-SQL Encryption Hierarchy key export files. In this function the black list filter that includes file system specific markers as identified in the same SQL Server 2008 R2 books Online article. The somewhat cumbersome PATINDEX() driven exclusion filter pattern is used in the file name function as is used for hardness testing.

1   -------------------------------------------------------------------------------
2   --    bwunder at yahoo dot com
3   --    Desc: apply file naming rules and conventions
4   --    name not already in use and no identified sql injection
5   -------------------------------------------------------------------------------
6   CREATE FUNCTION $(EHA_SCHEMA).CheckFile 
7     ( @Name VARBINARY (8000) )
8   RETURNS BIT
9   $(WITH_OPTIONS)
10  AS
11  BEGIN
12    RETURN (SELECT CASE WHEN  PATINDEX('%[#,.;:"'']%', Name) 
13                            + PATINDEX('%--%', Name)
14                            + PATINDEX('%*/%', Name)
15                            + PATINDEX('%/*%', Name)
16                            + PATINDEX('%DROP%', Name)
17                            + PATINDEX('%CREATE%', Name)
18                            + PATINDEX('%SELECT%', Name)
19                            + PATINDEX('%INSERT%', Name)
20                            + PATINDEX('%UPDATE%', Name)
21                            + PATINDEX('%DELETE%', Name)
22                            + PATINDEX('%GRANT%', Name)
23                            + PATINDEX('%ALTER%', Name) 
24                            + PATINDEX('%AUX%', Name) 
25                            + PATINDEX('%CLOCK$%', Name) 
26                            + PATINDEX('%COM[1-8]%', Name)
27                            + PATINDEX('%CON%', Name) 
28                            + PATINDEX('%LPT[1-8]%', Name) 
29                            + PATINDEX('%NUL%', Name) 
30                            + PATINDEX('%PRN%', Name) = 0
31                        AND NOT EXISTS 
32                ( SELECT COUNT(*) AS [Existing] 
33                  FROM $(EHA_SCHEMA).$(BACKUP_ACTIVITY_TABLE)
34                  WHERE BackupNameBucket = $(EHA_SCHEMA).AddSalt( '$(SPOKE_DATABASE)'
35                                                                , '$(EHA_SCHEMA)'
36                                                                , '$(BACKUP_ACTIVITY_TABLE)'
37                                                                , 'BackupNameBucket' 
38                                                                , Name ) )    
39                        THEN 1 ELSE 0 END
40            FROM (SELECT CAST( DECRYPTBYKEY ( @Name ) AS NVARCHAR(448) ) AS Name  
42                  FROM sys.certificates c
42                  JOIN sys.crypt_properties cp
43                  ON c.thumbprint = cp.thumbprint
44                  CROSS JOIN sys.database_role_members r
45                  WHERE r.role_principal_id = DATABASE_PRINCIPAL_ID ( '$(SPOKE_ADMIN_ROLE)' ) 
46                  AND r.member_principal_id = DATABASE_PRINCIPAL_ID ( ORIGINAL_LOGIN() )  
47                  AND c.name = '$(OBJECT_CERTIFICATE)'
48                  AND c.pvt_key_encryption_type = 'PW'
49                  AND cp.major_id = @@PROCID 
50                  AND @@NESTLEVEL > 1 
51                  AND IS_OBJECTSIGNED('OBJECT', @@PROCID, 'CERTIFICATE', c.thumbprint) = 1
52                  AND EXISTS (SELECT * FROM sys.database_role_members 
53                              WHERE [role_principal_id] = USER_ID('$(SPOKE_ADMIN_ROLE)')
54                              AND USER_NAME ([member_principal_id]) = SYSTEM_USER 
55                              AND SYSTEM_USER = ORIGINAL_LOGIN() ) ) AS derived );
56  END
57  GO
58  ADD SIGNATURE TO $(EHA_SCHEMA).CheckFile 
59  BY CERTIFICATE $(OBJECT_CERTIFICATE)
60  WITH PASSWORD = '$(OBJECT_CERTIFICATE_ENCRYPTION_PHRASE)';
61  GO

When processing happens one string at a time this filter is of small performance concern. However, processing a large set against such a filter could be slow and disruptive. The objects are obfuscated into the database WITH ENCRYPTION so only those with elevated access, development environment access and source repository access are likely to be aware of the filter details. Most of the logic in the functions is to verify the authority and authenticity of the caller and the calling object.

These functions demonstrate that fundamental SQL injection protection is easily achievable even for an application with the crippled regular expression support of T-SQL. If performance or load is a service level issue, the CLR might be a better host for the functions. However, as with obfuscation, the most important place to validate against SQL injection is at the point where data enters the system. In some cases SQL injection protection done after the invalidated text moves inside SQL Server will be too late. Only when the user interface is a SQL command line could it be the best security choice to validate against SQL injection inside SQL Server. In scope, SQL injection prevention is an application layer exercise. That being said, skipping the SQL injection validation inside SQL Server is reckless. Robust security will employ layers of defense.

In my mind, the command line too must always be considered as an attack vector even if not a favorite SQL injection attack vector at this time and even if the application makes no use of the command line. As the metamorphosis of now soluble security landscape unfolds, the hackers will be shining their cyber-flashlights everywhere and chasing anything shiny. To discount that the command line will continue to get a good share of malicious attention as long as there are command lines and hackers is negligence and/or denial.

For the Encryption Hierarchy Administration schema that uses the functions above a Powershell deployment and administration interface is helpful to improve security. With a pure T-SQL approach there is always a risk of exposure of user input text of secrets in memory buffers before the input value can be ciphered by the database engine. Granted, it is a brief period of time and I am not even sure how one would go about sniffing SQLCMD command line input without running in a debugger or waiting for the input to move into database engine workspace. It surely must be available somewhere in memory. The scenario is a target. I know I have never check if the operating system is running a debugger in any T-SQL script I have ever written. This helps to illustrate why the best time and place to encrypt data is at the time it is generated in the place where it is generated or enters the system. Even then, 100% certainty will remain elusive if the system cannot be verified to be keylogger free.

The utility models a somewhat unusual scenario where encryption at the database is the right choice. Nonetheless, getting the many secrets required for the administration of encryption keys and key backups entered into the system presents a potential for exposure to memory mining hackers. Using SecureString input and SecureString based SMO methods to instantiate the database objects that need the secrets can eliminate much of that vulnerability. As you may know a SecureString is an .NET object .encrypted by a hash from the current user's session at all times while in memory with user cleanup from memory that can be more secure than garbage collection. It is relatively easy for the user to decrypt the SecureString data on demand but doing so would result in sensitive information becoming available as clear text in memory registers where the un-encrypted copy is written. No other users have access to the encryption key.

  
function Decode-SecureString 
{   
    [CmdletBinding( PositionalBinding=$true )]
    [OutputType( [String] )]
    param ( [Parameter( Mandatory=$true, ValueFromPipeline=$true )]
            [System.Security.SecureString] $secureString )  
    begin 
    { $marshal = [System.Runtime.InteropServices.Marshal] }
    process 
    { $BSTR = $marshal::SecureStringToBSTR($secureString )
     $marshal::PtrToStringAuto($BSTR) } 
    end
    { $marshal::ZeroFreeBSTR($BSTR) }
}

Decode-EHSecureString $( ConvertTo-SecureString '1Qa@wSdE3$rFgT'  -AsPlainText -Force )

Powershell obfuscates Read-Host user input of type SecureString with the asterix (*) on the input screen. With the ISE you get a WPF input dialog that more clearly show the prompt but could also become annoying for command-line purists.

To evaluate the use of a Powershell installer, I coded a Powershell installation wrapper for the hub database installation scripts of the utility. The hub database needs 4 secrets: the passwords for four contained database users.  With this change it makes no sense to add an extra trip to the database to evaluate the hardness and SQL injection vulnerability for each secret. Instead, the SQL injection input validation logic from the T-SQL functions above it migrated to a Powershell Advanced Function - Advanced meaning that the function acts like a CmdLet - that accepts a SecureString.

  
1  function Test-EHSecureString 
2  {   
3   [CmdletBinding( PositionalBinding=$true )]
4      [OutputType( [Boolean] )]
5      param ( [Parameter( Mandatory=$true, ValueFromPipeline=$true )] 
6              [System.Security.SecureString] $secureString
7            , [Int32] $minLength = 14 
8            , [Int32] $minScore = 3 )  
9      begin 
10     { 
11         $marshal = [System.Runtime.InteropServices.Marshal] 
12     }
13     process 
14     {   # need the var to zero & free unencrypted copy of secret
15         [Int16] $score = 0
16         $BSTR = $marshal::SecureStringToBSTR($secureString)
17         if ( $marshal::PtrToStringAuto($BSTR).length -ge $minLength )
18         { 
19             switch -Regex ( $( $marshal::PtrToStringAuto($BSTR) ) )
20            {
21             '[#,.;:\\]+?' { Write-Warning ( 'character: {0}' -f $Matches[0] ); Break }
22             '(DROP|ADD|CREATE|SELECT|INSERT|UPDATE|DELETE|GRANT|REVOKE|RUNAS|ALTER)+?' 
23                           { Write-Warning ( 'SQL command: {0}' -f $Matches[0] ); Break }
24             '(AUX|CLOCK|COM[1-8]|CON|LPT[1-8]|NUL|PRN)+?' 
25                           { Write-Warning ( 'dos command: {0}' -f $Matches[0] ); Break } 
26             '(--|\*\/|\/\*)+?'{ Write-Warning ( 'comment: {0}' -f $Matches[0] ); Break }
27             '(?-i)[a-z]'  { $score+=1 }
28             '(?-i)[A-Z]'  { $score+=1 }
29             '\d+?'        { $score+=1 }
30             '\S\W+?'      { $score+=1 }
31             Default { Write-Warning $switch.current; Break }        
32            } 
33         }
34         else
35         { write-warning 
36                      ( 'length: {0}' -f $( $marshal::PtrToStringAuto($BSTR).length ) ) } 
37         write-warning ( 'score: {0}' -f $score )  
38         $( $score -ge $minScore )
39     }        
40     end { $marshal::ZeroFreeBSTR($BSTR) }
41 }

One thing for sure. Much less code required in Powershell than T-SQL to create a user. To securely invoke the function a Read-Host -AsSecureString prompts for user input that will go into the memory location allocated to the SecureString and only as encrypted data. Here the Powershell script will prompt for input until it gets an acceptable value. Remember, no one else will be able to decode this value in memory. Only the user that created the SecureString. Defense-in-Depth demands that care is be taken that the SecureString memory location is not taken for an off-line brute force interrogation.

 

do { $SQL_PASSWORD = $(Read-Host 'SQL_PASSWORD?' -AsSecureString ) } 
until ( $(Test-SecureStringHardness $HUB_ADMIN_PASSWORD ) )

Then the database is affected by the entered secret using SMO. In this case a user with password will be created in a contained database.

  
if ( $( Get-ChildItem -Name) -notcontains 'HubAdmin' )
{
    $HubAdmin = New-Object Microsoft.SqlServer.Management.Smo.User
    $HubAdmin.Parent = $smoHubDB
    $HubAdmin.Name = 'HubAdmin'     
    $HubAdmin.Create( $HUB_ADMIN_PASSWORD ) 
}

The Test-SecureString function does expose the clear text of the secret in the PSDebug trace stream during the switch operation as $switch. To my knowledge there is no way to obfuscate the value. On top of that the disposal of the $switch automatic variable is under garbage collection so there is no reliable way to know for sure when you can stop wondering is anyone found it. That uncertainty may be more of a risk than the SQLCMD exposure that the secure string is supposed to solve? On the other hand, the risk of exposure of the SQLCMD setvar values is undetermined so it would be silly to pretend to quantify an unknown risk. What I know for sure is those values have to touch primary storage buffers in order to load the variables and then populate the SQLCMD - $(VARIABLE_NAME) - tokens in the script. At least with the Powershell script I can quantify the risk and take all necessary precaution to mitigate. With SQLCMD setvar variables about all I can do to be certain my secrets are not fished out of the free pool or where ever else they might be buffered as clear text is remove the power. Even that is no guarantee the secrets are not leaked to a paging file, spooler or log while exposed internally or externally as clear text as the system shuts down.

At this point I'm convinced that it is best to validate Powershell SecureString input against SQL injection threats. The risk that someone will find the secrets in local memory and use them with malicious intent is far less than the risk from SQL injection in my estimation. I will continue to integrate Powershell into the install script with the goal of  using a Powershell installer. This is a much better input scenario than the T-SQL event obfuscation technique I had been using.

I will leave the SQL injection filters in the T-SQL functions to complement the Powershell filter for two reasons. Defense-in-depth and [sic]Defense-in-depth. 

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